Low-Coordinate Bismuth Cations - Inorganic Chemistry (ACS

Mar 17, 2014 - School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand. § Department of Chem...
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Low-Coordinate Bismuth Cations Ryan J. Schwamm,† Benjamin M. Day,§ Martyn P. Coles,*,† and Christopher M. Fitchett‡ †

School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand Department of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, U.K. ‡ Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch 8041, New Zealand §

S Supporting Information *

ABSTRACT: Chloride abstraction from the diamido-bismuth compound Bi(Me2Si{NAr}2)Cl (1, Ar = 2,6-i-Pr2C6H3) using MCl3 (M = Al, Ga) is a facile route to cationic species. Stoichiometric reactions afford the tetrachlorometallate salts [Bi(Me2Si{NAr}2)][MCl4] (2a, M = Al; 3a, M = Ga), whereas reaction with 0.5 equiv of the group 13 reagent gives the μchlorido bridged cations [{Bi(Me2Si{NAr}2)}2(μ-Cl)][MCl4] (2b, M = Al; 3b, M = Ga). The crystal structure of 2a shows a formally two-coordinate bismuth cation, with a Bi···Cl contact to the [AlCl4]− anion, whereas the structure of 3b shows a total of three Bi···Cl contacts to [GaCl4]−. Both species associate as {1:1}2 dimers in the solid state through additional Bi···Cl interactions. Attempted preparation of cationic complexes using either NaBR4 (R = Ph, Et) or [HNEt3][BPh4] were unsuccessful. Instead of forming the borate salts, the neutral compounds Bi(Me2Si{NAr}2)R (4, R = Et; 5, R = Ph) were isolated as a result of aryl/alkyl transfer from boron to bismuth.

1. INTRODUCTION Commercially available BiX3 compounds (X = halogen, triflate, nitrate) are used as Lewis acidic reagents to promote a range of organic transformations1 and polymerization reactions.2 More recently cationic bismuth compounds have been investigated,3,4 developing the concept that an increased electrophilicity associated with the positively charged metal center will enhance the activity of the reagents. Due in part to the large radius of the element [Shannon ionic radii Bi3+: 6-coordinate = 1.03 Å; 8-coordinate = 1.17 Å],5 much of the research on cationic bismuth compounds has focused on the application of multidentate ligands able to provide additional interactions to support the metal center.6 Prominent among these examples are the potentially tridentate systems based on either a dianionic (C,E,C) framework (E = N, O, S),4,7 or the monoanionic (E,C,E)-system.8,9 Relatively little work has been directed toward the study of low-coordinate bismuth cations. A survey of the Cambridge Structural Database10 was conducted to examine the distribution of coordination numbers associated with crystallographically characterized cationic bismuth compounds. The results, displayed in Figure 1, were divided into three classes: bismuth(III), bismuth(V), and bismuth clusters (defined in this survey as species containing three or more Bi atoms). Most examples have been reported in which the bismuth is 4-coordinate (52.5%), with 6- and 8coordinate bismuth each representing 12.0% of the total number of structures listed in the database. Both high- (>8-coordinate: 7.6%) and especially low- ( 2σ(I) data/restraints/parameters final R indices [I > 2σ(I)] final R indices (all data) GOF on F2 largest diff. peak/hole [e Å−3] a

2a

3b·C6H14

2(4)·C7(H8)

5

C26H40AlBiCl4N2Si 786.45 173(2) 0.08 × 0.08 × 0.01 orthorhombic Pbcn (No.60) 24.9726(10) 16.6486(4) 16.1717(6) 90 90 90 6723.5(4) 8 1.55 5.64 7.02 to 54.16 26421 7374 [Rint 0.161] 4578 7374/0/316 R1 = 0.077, wR2 = 0.163 R1 = 0.131 wR2 = 0.189 1.018 3.64 and −3.18a

C58H94Bi2Cl5GaN4Si2 1568.48 120.01(10) 0.10 × 0.08 × 0.02 triclinic P1̅ (No.2) 12.8472(5) 17.0713(7) 17.4081(7) 117.739(4) 92.142(3) 90.447(3) 3375.4(3) 2 1.54 12.97 2.87 to 74.00 26092 13265 [Rint 0.034] 11200 13265/36/671 R1 = 0.031, wR2 = 0.073 R1 = 0.040, wR2 = 0.080 1.036 1.66 and −2.15

C135H180Bi4N8Si4 2863.15 120.02(10) 0.35 × 0.16 × 0.05 triclinic P1̅ (No.2) 12.9068(2) 15.6323(4) 17.3240(5) 108.940(2) 93.6783(18) 100.2794(18) 3224.91(14) 1 1.47 5.53 5.32 to 60.0 66037 18799 [Rint 0.035] 15967 18799/0/714 R1 = 0.024, wR2 = 0.053 R1 = 0.033, wR2 = 0.056 1.036 1.82 and −0.97

C28H45BiN2Si 646.73 120.0 0.21 × 0.15 × 0.14 trigonal R3̅ (No.148) 28.7503(11) 28.7503(11) 9.8541(5) 90 90 120 7053.9(6) 9 1.37 5.67 5.66 to 66.22 16452 5348 [Rint 0.072] 4288 5348/114/179 R1 = 0.129, wR2 = 0.272 R1 = 0.151 wR2 = 0.280 1.323 1.88 and −3.13

Close to Bi.

Bi−Cl distances are longer than the terminal chloride bonds in 1 and shorter than the closest Bi···Cl ion-contact in 2a, suggesting an intermediate bonding type with delocalization across the Bi−Cl−Bi moiety. The asymmetry is in good agreement with the only other structurally characterized mono chloride-bridged cation, [{t-BuN(CH2C6H4)2Bi}2(μ-Cl)][B(C6F5)4],7 for which ΔBiCl = 0.11 Å. As noted for 2a, there is no significant decrease in Bi−N bond lengths upon generation of the cation, and the Bi atoms are essentially coplanar with the chelating diamide (deviation from the N2Si least-squares plane = 0.088(8) and 0.050(7) Å for Bi1 and Bi2, respectively), generating relatively large ligand bite angles of 72.08(15)° and 72.21(15)°. The interion Bi···Cl distances in the asymmetric unit of 3b span the range of 3.3168(2)−3.5618(2) Å and are considerably shorter than they are in the crystal structure of IV in which no bismuth-to-tetrachlorogallate contacts are described.15 Two of the interactions in 3b involve Bi2, also consistent with this being the more positive metal. The Ga−Cl bond lengths (range from 2.1622(14) Å to 2.1878(14) Å) span those reported for IV and the series of [M(crown)n(THF)m][GaCl4] compounds (M = Li/Na, crown = 12-c-4, n = 2, m = 0; M = Na, crown = 18-c-6, n = 1, m = 0; M = K, crown = 18-c-6, n = 1, m = 2).25 The difference in the Ga−Cl bond lengths within the anion (ΔGaCl = 0.03 Å) is considerably smaller than the corresponding difference in the Al−Cl distances of 2a, consistent with all four chlorides being involved in Bi···Cl interactions. Indeed, examination of the unit cell of 3b confirms that Cl4 is associating with a second cation (Cl4···Bi1′ 3.3277(1) Å) to generate the {1:1}2 aggregate bis{μ-chlorido-[N,N′dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-1κN)][N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido2κN)]dibismuth(1+)}deca-μ-chlorido-1:3κ4Cl,1:4κ2Cl,1:5κ2Cl,

There is a relatively large range of Al−Cl bond lengths in the tetrachloroaluminate anion (ΔAlCl = 0.08 Å), reflecting differing degrees of Bi···Cl interaction. The longest Al−Cl bond (2.172(4) Å) involves chloride Cl1, which is most closely associated with the bismuth. The shortest bond (Al−Cl2, 2.091(5) Å) is at the low end of the range noted for a series of noncoordinated [AlCl4]− anions within the structurally characterized compounds [M(crown)n(THF)m][AlCl4] (M = Li/Na, crown =12-c-4, n = 2, m = 0; M = Na/K, crown =18-c-6, n = 1, m = 2; M = K, crown =15-c-5, n = 2, m = 0: range of Al−Cl bond lengths = 2.102(2)−2.1469(9) Å),22 consistent with a terminal chloride ligand. The remaining Al−Cl bonds are intermediate between these two values and involve chlorides that are engaged in intermolecular Bi···Cl interactions to another cation, resulting in an overall {1:1}2 molecular structure (Figure 5). The bonding mode of the [AlCl4]− anion in hexa-μ-chlorido-1:3κ4Cl,1:4κ2Cl,2:3κ2Cl,2:4κ4Cl-dichlorido1κCl,2κCl-[N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-3κN)][N,N′-dimethylsilanediylbis(2,6-dipropan-2ylphenylamido-4κN)]dialuminiumdibismuth ([2a]2) is unusual, but has been previously observed in polymeric tin23 and samarium24 complexes. The bismuth component of the tetrachlorogallate salt 3b consists of a μ-chlorido-bridged monocation in which each pyramidal Bi atom retains a bidentate diamido-ligand. The interplanar angle between the SiN2Bi metallacycles is 144.03(11)° with a trans−trans arrangement of the ligands with respect to Si···Bi−Cl−Bi···Si. This unit is supported by three Bi···Cl interactions to the [GaCl4]− anion (Figure 6). The Bi−Cl1 bond lengths within the cation are inequivalent (2.7888(12) and 2.6902(12) Å to Bi1 and Bi2, respectively; ΔBiCl = 0.10 Å), suggesting a localization of positive charge on Bi2. Both of the E

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Table 2. Selected Bond Lengths (Å) for 2a and 3b, Presented with Those of 1 for Comparison

1a Bi−N

2.132(3) 2.144(3) 2.181(3)

Bi−Cl

2.4857(16) 2.5560(10)

Bi···Cl

Si−N

N−Si−N Bi−N−Si

N−Bi−Cl

a

3bc

2.118(8) 2.120(8)

2.121(4) 2.131(3) 2.143(3) 2.152(3) 2.6902(12) 2.7888(12) 3.3168(14) 3.3277(13) 3.5373(16) 3.5618(14) 1.734(4) 1.736(4) 1.748(4) 1.752(4) 2.1622(14) 2.1689(15) 2.1770(13) 2.1878(14) 72.08(15) 72.21(15) 92.67(17)

2.953(3)

1.733(3) 1.735(3) 1.736(3)

M−Cl

N−Bi−N

2ab

70.74(16) 71.78(11) 92.58(15) 93.3(2) 97.17(14) 97.54(13) 97.71(14) 96.34(9) 96.37(9) 97.89(9)

1.763(9) 1.765(8)

2.091(5) 2.134(4) 2.152(4) 2.172(4) 73.7(3) 92.1(4) 97.1(3) 97.0(3)

94.2(2) 98.1(2)

Figure 6. Thermal ellipsoid plot (30% probability, H-atoms and hexane solvate omitted) of [{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] (3b).

[N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido4κN)][N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-5κN)][N,N′-dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-6κN)]digalliumtetrabismuthate(2-) in the solid state ([3b]2, Figure 7). This is the only structurally characterized

97.00(17) 97.64(18) 97.88(18) 98.16(17) 94.28(11) 97.56(11) 97.76(10) 101.12(11)

1.5 molecules in the unit cell. bM = Al. cM = Ga.

Figure 7. Molecular structure of [3b]2, showing the bridging [GaCl4]− anions (′ = −x, −y, −z; aryl groups reduced to show only ipso-carbon atoms).

example of the tetrachlorogallate anion interacting through all four chloride ligands. 3.2. Reaction with M[BR4] (M = Na, R = Ph, Et; M = HNEt3, R = Ph). Evans and co-workers have shown that the bis(aryl) bismuth chloride compound BiAr′2Cl (Ar′ = 2,6(Me2NCH2)2C6H3) is converted to the tetraphenylborate salt upon reaction with NaBPh4 (Scheme 2). The cation is also generated from the protonolysis reaction of the allyl compound BiAr′2(CH2CHCH2) with [HNEt3][BPh4].9 Monitoring a mixture of 1 and NaBPh4 by 1H NMR spectroscopy indicated that the reaction did not proceed at room temperature. Heating the reaction to 90 °C for 3 d, however, afforded a mixture of yellow 4 and colorless crystals upon workup. Physical separation allowed pure samples of 4 to be prepared for analysis by NMR spectroscopy, elemental analysis, and X-ray diffraction. 1 H NMR data for 4 indicate a C1 symmetry structure, with SiMe2 resonances at δH 0.63 and 0.15 ppm. Integration of the aromatic region of the spectrum is consistent with the presence

Figure 5. Molecular structure of [2a]2, showing the bridging [AlCl4]− anions (′ = 1 − x, y, 1/2 − z; aryl groups reduced to show only ipsocarbon atoms).

1:6κ 2 Cl,2:4κ 2 Cl,2:5κ 2 Cl,2:6κ 4 Cl,3:4κ 2 Cl,5:6κ 2 Cl-[N,N′dimethylsilanediylbis(2,6-dipropan-2-ylphenylamido-3κN)]F

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Scheme 2. Reaction of Bi(Me2Si{NAr}2)X (1 X = Cl, 5 X = Et) with [A][BR4] (A = Na, R = Ph, Et; A = HNEt3, R = Ph)a

a

(i) NaBPh4; (ii) NaBEt4; (iii) [HNEt3][BPh4].

of a single phenyl group, with the peaks assigned to the orthoprotons at low field (δH = 8.48 ppm, C6D6). This chemical shift is significantly different from that observed for the [BPh4]− anion (e.g., [Bi(Ar′)2][BPh4]: δH = 6.99 ppm, CD3CN9) and BiPh3 (δH = 7.73 ppm, C6D6). These data are consistent with formation of the phenyl compound Bi(Me2Si{NAr}2)Ph, confirmed by elemental analysis and an X-ray crystal structure determination (vide inf ra). The colorless crystals that formed during the reaction were identified as BPh3 by 11B NMR spectroscopy (δB 68 ppm26) and by comparison of their unit cell with published data.27 Aryl transfer reactions from [BAr4]− anions are well documented,28 and the reaction of Na[BAr4″] (Ar″ = Ph, p-tolyl, 4−F-C6H4) with bismuth(III) carboxylates has been reported recently as a convenient route to BiAr3″ species.29 To probe this mode of reactivity further we examined the reaction of 1 with Na[BEt4], where the tetraethylborate anion is known to behave as an alkyl transfer reagent.30 In this case the reaction proceeded at room temperature, affording pale yellow crystals on workup. 1H NMR data was consistent with the bismuth ethyl compound Bi(Me 2 Si{NAr}2 )Et (5) showing a C 1 symmetry (SiMe2: δH = 0.42 and 0.04 ppm). The resonances for methyl and methylene groups of the ethyl ligand appear as a triplet and quartet at δH 2.47 and 2.04 ppm, respectively. The 29 Si NMR resonances for 4 (δSi = 19.5 ppm) and 5 (δSi = 17.8 ppm) are shifted to higher field compared with 1 (ΔδSi = −10.2 ppm and −11.9 ppm, respectively), reflecting the relatively electron-rich metallacycle upon exchanging the bismuth substituent from chloride to aryl/alkyl groups. The structures of 4 and 5 were determined by single-crystal X-ray diffraction experiments (Tables 1 and 3; Figures 8 and 9).

Figure 8. Thermal ellipsoid plot (30% probability) of Bi(Me2Si{NAr}2)Et, 5 (′ = 1 − x, 1 − y, −z; H-atoms omitted).

Figure 9. Thermal ellipsoid plot (30% probability) of one of the independent molecules of Bi(Me2Si{NAr}2)Ph, 4 (H-atoms and toluene solvate omitted).

small energy difference between the two orientations of the metallacycle with respect to the aryl substituents. As a result the solution of the data is not of sufficient quality for a meaningful discussion of bond lengths and angles; it does, however, confirm the connectivity of 5 as a rare example of a monomeric bismuth-ethyl compound (Figure 8).31 Compound 4 crystallizes as the toluene solvate, with two independent molecules in the unit cell that differ primarily with respect to the orientation of the phenyl substituent (Figure 9). Each molecule is monomeric with a pyramidal geometry of the Bi atom and an essentially planar metallacycle (deviation of Bi from mean SiN2 plane: Bi1 0.121(4) Å, Bi2 0.037(4) Å). The Bi−N bond lengths in 4 are longer than in the other structures examined during this study, resulting in a smaller average bite angle of 70.68(7)° for the diamide ligand. The Bi−C bond length (2.253(3) Å) is unexceptional and is within the range noted for BiPh3 (2.237(7) to 2.273(8) Å).32 Comparing the two molecules within the unit cell we note that phenyl groups are rotated in opposite directions along the Bi−Cipso bond relative to the plane bisecting the metallacycle through the silicon, bismuth, and Cipso atoms (molecule Bi1 = +14.85(7)°; molecule Bi2 = −29.56(11)°, where +ve = clockwise directionFigure 10a,b). This twisted orientation brings the portion of the phenyl group located below the metallacycle into close proximity with one of the i-Pr groups of the aryl substituents. The resulting steric conflict is alleviated by the nitrogen

Table 3. Selected Bond Lengths (Å) and Angles (deg) for 4 Bi1−N1 Bi1−N2 Bi1−C27 Si1−N1 Si1−N2 N1−Bi1−N2 N1−Bi1−C27 N2−Bi1−C27 Bi1−N1−Si1 Bi1−N2−Si1 N1−Si1−N2

2.168(2) 2.177(2) 2.253(3) 1.713(2) 1.726(2) 70.50(7) 98.02(9) 100.50(9) 98.21(9) 97.49(9) 93.65(10)

Bi2−N3 Bi2−N4 Bi2−C58 Si2−N3 Si2−N4 N3−Bi2−N4 N3−Bi2−C58 N4−Bi2−C58 Bi2−N3−Si2 Bi2−N4−Si2 N3−Si2−N4

2.1790(19) 2.172(2) 2.252(3) 1.721(2) 1.731(2) 70.86(7) 100.32(8) 97.44(9) 97.63(9) 97.59(9) 93.90(10)

Unfortunately the data solution for compound 5 was complicated by molecular disorder that was modeled in the R3̅ space group as being about an inversion center (Supporting Information, Figure S2). This disorder is most likely caused by the small size of the ethyl substituent compared to other X-groups in the Bi(Me2Si{NAr}2)X compounds, resulting in a G

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4. DISCUSSION The paucity of low-coordinate bismuth cations is illustrated by the facts that 2a is only the second formally two-coordinate Bi+ center to be structurally characterized and that 2a is a derivative of the first example.11 This is perhaps not surprising given the large radius of the element and the focus on multidentate ligands in this area of chemistry. As a consequence, additional interion (and other intermolecular) interactions become important in the condensed (solid) state, as shown by the Bi···Cl contacts present in the structures of 2a and 3b. Previous work has quantified the bond order (BO) of Bi···Cl interactions (eq 1),34 using values of r0 = 2.423 Å35 and B = 0.39.36 We recently used this equation to show that the intermolecular Bi···Cl BO between associated molecules in the trimeric unit of 1 was 0.1418 and that this was significantly less than that calculated for a similar Bi···Cl interaction in the Nt-Bu analogue (BO = 0.20).37 Table 4 summarizes a series of BOs for some bismuth chloride compounds and the corresponding cations, generated by halide abstraction using MCl3 (M = Al, Ga). ⎡ (r − r ) ⎤ BO = exp⎢ 0 ⎥ ⎣ B ⎦

(eq 1)

According to eq 1, the terminal bismuth chloride bonds in 1 have BOs of 0.85 and 0.71, reflecting the relatively long Bi−Cl distances. The smaller BO (weaker bond) corresponds to the chloride involved in bridging interactions to another molecule, showing the sensitivity of this measurement to small changes in the environment of the bond. Given that these Bi−Cl BOs are significantly less than unity, it is perhaps not surprising that chloride abstraction and generation of bismuth cations is a relatively facile process. Conversion of 1 to the cation and association of the formally positive bismuth metal and the tetrachloroaluminate anion gives a BO of 0.26 for the primary Bi···Cl interaction, suggesting a strongly associated ion pair in the solid state with a reduction of ∼0.5 on generation of the cation (ΔBO = −0.59 and −0.45). Unfortunately, it is not possible to make a direct comparison with the ΔBO in the corresponding Nt-Bu cation (I, Figure 2), as the primary Bi−Cl bond in the neutral compound (BO = 0.43) is already weakened by intermolecular interactions along a 1-D chain in the crystal structure (vide supra). Nevertheless a reduction is observed upon generation of the cation, with the principal Bi···[Cl−AlCl3] BO of 0.19 in this case approximately equal to the weaker Bi−Cl···Bi bridging bond along the chain. The calculated BO values for the Bi··· [Cl−AlCl3] interactions of the associated dimer in 2 (Figure 5) are 0.11 and 0.04 for Cl4 and Cl3, respectively. These values indicate weak, nonsymmetrical bonding to the second bismuth cation with values lower than the major interion interactions in I. Comparing these BOs with the corresponding values for other ligand systems shows that the ΔBOs upon cation generation are highly dependent on the ligand. For example, the bulky cyclopentadienyl derivative [Bi(Cp″)Cl2]2 has BO values of 0.75 for the terminal Bi−Cl bonds, with the BOs of the nonsymmetrical bridging μ-chlorides being 0.53 and 0.19 (average from two crystal modifications). Formation of the cation retains the dimeric unit, with only minor modifications to the Bi(μ-Cl)Bi BOs (0.57 and 0.20), and the closest contact to the [AlCl4]− corresponding to a BO of 0.06.

Figure 10. Schematic representations of the two molecules of 4, showing (a) the different rotation of the phenyl ligand relative to the Si···Bi−Cipso vector, (b) the displacement of one of the aryl groups out of the plane of the metallacycle, and (c) the dimerization of molecule Bi2 (′ = 2 − x, −y, 1 − z).

aryl-substituent being located above the BiNSiN-plane, illustrated by the different angles that the N−Cipso bonds adopt with respect to this plane (molecule Bi1: N1−C1 = 5.9°, N2−C13 = 15.3°; molecule Bi2: N3−C34 = 9.3°, N4−C46 = 21.2°; see Supporting Information, Figure S3). The twisting of the phenyl ligand is more pronounced in molecule Bi2. Examination of the packing shows that this molecule is involved in intermolecular interactions with a symmetry generated equivalent positioned about an inversion center (Figure 10c). The para-carbon atom of the phenyl substituent (C61) is located at 3.629(3) Å from Bi2′ (′ = 2-x, -y, 1-z), within the range of distances previously attributed to a bonding interaction within the series of compounds [BiCl3·(C6H6‑nMen)] (Bi···C distances 3.168(7) to 3.751(8) Å).33 However, the large ring slippage of 2.57 Å from the centroid of the C6-ring suggests that it is the π−π interactions between the two phenyl rings that dominate (centroid−centroid distance 3.827(3) Å, plane-to-plane shift 1.295(5) Å), although the role of crystal packing forces should not be dismissed. H

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Table 4. Bond Orders (BOs) for Bi−Cl Bonds and Bi···Cl Interactions, Calculated Using eq 1 compound

Bi−Cl

[Bi]···[Cl-MCl3]

bond order (BO)

bond order (BO)

[Bi(Me2Si{NAr}2)Cl]3a (1)

0.85 0.71 0.14 (μ-)

[Bi(Me2Si{NAr}2)][AlCl4] (2a)

[Bi(Me2Si{Nt-Bu}2)Cl]∞

0.26 0.11 0.04 0.43 (μ-) 0.20 (μ-)

[Bi(Cp″)Cl][AlCl4] Bi(N{SiMe3}N{SiMe3}2)2Cl [Bi(N{SiMe3}N{SiMe3}2)2][GaCl4] (IV) [{Bi(Me2Si{NAr}2)}2(μ-Cl)][GaCl4] (3b)

a

0.19 0.17 0.03 0.02 0.75/0.74 0.48/0.57 (μ-) 0.22/0.16 (μ-) 0.57 (μ-) 0.20 (μ-) 0.77

■

0.06 0.06 0.03 0.03 0.10 0.10 0.06 0.05

■

The tetrachlorogallate salt 3b has a nonsymmetrically bridging chloride in the cationic unit, with BOs of 0.50 and 0.39. Despite being aligned well within the dimeric unit (Figure 7), the interion BOs for Bi···[Cl−GaCl3] are only 0.10 to 0.05, indicating a weak interaction. These are only slightly more than the calculated BOs of 0.03 in [Bi(N{SiMe3}N{SiMe3}2)2][GaCl4] (IV). In summary, the BOs associated with terminal Bi−Cl bonds in neutral species are significantly less than those expected for a single bond, being typically in the range of 0.7−0.8. In contrast the intermolecular BOs calculated for Bi−Cl···Bi bridges during the formation of μ,μ-dichlorobridged dimers can be as much as ∼0.55 and during the association of neutral molecules can be up to ∼0.43. Surprisingly, formation of “contact” ion pairs does not give such large values of BO between the Bi+ center and the tetrachloroaluminate anion, despite the electrostatic attraction between the ions. This is may be due to a delocalization of the positive charge into the ancillary ligands at Bi (as noted for the N,N′,N′-tris(trimethylsilyl)hyradzido salt IV) and the relative exposure of the (long) terminal Bi−Cl bonds compared with the much shorter Al−Cl bonds.

11

14, 38

0.50 (μ-) 0.39 (μ-)

Two different crystal modifications; Cp″ = [1,2,3,4-iPr4C5H]−.

this work

37

[Bi(Me2Si{Nt-Bu}2)][AlCl4] (I)

[Bi(Cp″)Cl2]2a

reference 18

14 15 15 this work

AUTHOR INFORMATION

Corresponding Author

* E-mail: [email protected]. Phone: +64 (0)4 4636357. Author Contributions

The manuscript was written through contributions of all authors. Funding

Victoria Master’s by thesis scholarship (R.J.S.) Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Dr. Richard Hartshorn for help in naming compounds 2a and 3b using the correct “kappa” nomenclature, as currently defined by IUPAC.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

Alternative solution-state structures for a C2h ligand environment; additional projections of the crystal structures of 4 and 5; crystallographic information files (CIF format) for 2a (CCDC 990963), 3b (CCDC 990964), 4 (CCDC 990965), and 5 (CCDC 990966). This material is available free of charge via the Internet at http://pubs.acs.org. I

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Inorganic Chemistry

Article

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